I would say, yeah, it's good for moderate gaming. They're affordable too. If you can't afford a higher price video card, the 8600GT is not bad at all.
As for the RAM, it depends what you are doing. Basic stuff besides gaming and such, you probably won't notice too much difference. I've used lower speed RAM before and I persoanlly don't feel a significant increase in performance. Specwise, you will pick up speed--but in reality, not feeling it a great deal. It's probably psychological with me. But, adding more RAM does make a huge difference.
*Fact: Microsoft Window's Blue Screen of Death vs Computerforums.org's White Screen of Death. Which is worse?